There is a component in the fuel system on the frame under the drivers side that the book does not show .it is where you would usually find a file filter but this isn't a filter it has a cap on it and when you remove it it is full of fuel . I dumped it out and it runs fine for 20 miles then it drops to 15 mph and runs ruff

 

Does this van have 2 tanks

 

If you have dual tanks, it's your dual function reservoir (DFR) or also called the tank select valve.There may also be a high pressure fuel pump in that area too.